Effect of dl-3-n-butylphthalide on the size of infarction and behavior changes were investigated after delayed neuronal damage in rats subjected to permanent middle cerebral artery occlusion (MCAO) by the method of Tamura et al, and the scores of behavior were evaluated by the method of Bederson et al. The results show that the size of infarct area was significantly reduced 2 h after MCAO following administration of NBP at the dose of 80, 160 and 240 mg.kg-1, the percentage of reduction of infarct area was 49.0%, 69.5% and 85.1% respectively. Neurological deficit was also improved. The size of infarction and the score of neurological deficit were also reduced significantly following pretreatment with NBP at the dose of 80 mg.kg-1 per day for 7 days by the end of the final dosage 24 h before MCAO or at the single dose of 160 mg.kg-1 1 h before MCAO. The results suggest that NBP has therapeutic and preventive effect on stroke and imply that NBP has the action of attenuating neuronal damage after delayed cerebral injury. In addition, the level of calcium ([Ca2+]i) in rat intrasynaptosomes was determined using fura-2 (a fluorescence indicator) technique. It was found that NBP can not lower the rise of [Ca2+]i induced by 30 mmol.L-1 KCl. However, the effect of NBP on [Ca2+]i overload induced by excitatory amino acid remains to be studied.